Squamous cell carcinoma (SCC) is a common form of skin cancer that originates from squamous cells, which are flat cells found in the outermost layer of the skin. It typically appears on areas frequently exposed to the sun, such as the head, neck, and hands. While SCC is widely recognized, its potential to spread to other parts of the body, known as metastasis, is relatively uncommon, especially when identified and treated at an early stage.
Understanding the Likelihood of Spread
The risk of squamous cell carcinoma spreading is generally low, with the vast majority of cases remaining localized. The overall metastatic rate for cutaneous SCC is reported to be between 1.2% and 5%. This low rate is often attributed to early detection and effective treatment strategies. The likelihood of spread increases if the SCC is invasive, meaning it has grown beyond the top layer of the skin into deeper tissues. When SCC is diagnosed and treated promptly, the prognosis is favorable, with a high survival rate. If left untreated, SCC can grow deeper and potentially spread, making treatment more challenging.
Factors Influencing Spread
Several characteristics of the tumor and patient factors can influence the risk of SCC spreading:
Tumors larger than 2 centimeters in diameter or those with a depth of invasion greater than 2 millimeters carry a higher risk of metastasis. Tumors that invade beyond the subcutaneous fat also show a significantly increased risk.
Location on the lips, ears, anogenital area, or arising in chronic wounds or scars.
Aggressive histological features, such as poor differentiation of cancer cells or perineural invasion (spread along nerves).
A weakened immune system, as seen in organ transplant recipients or individuals with certain medical conditions.
Common Sites of Metastasis
When squamous cell carcinoma spreads, it most frequently travels to nearby lymph nodes, known as regional metastasis. Lymph nodes in the neck, armpits, and groin are common sites for regional involvement. Distant metastasis, where the cancer spreads to organs far from the original tumor site, is rarer than regional spread. If distant metastasis occurs, the most common organs affected include the lungs, bones, and liver. These occurrences represent a more advanced stage of the disease.
Detecting and Monitoring Spread
Healthcare professionals use several methods to detect and monitor for SCC spread. Regular clinical examinations involve thorough skin checks and careful palpation of regional lymph nodes. Any concerning lesions or enlarged lymph nodes may require a biopsy, where a small tissue sample is taken for microscopic examination to confirm the presence of cancer cells.
Imaging studies are employed in specific situations, particularly for high-risk cases or when metastasis is suspected. Computed tomography (CT) scans are useful for evaluating regional lymph node involvement and detecting bone invasion. Magnetic resonance imaging (MRI) provides detailed soft tissue views and is particularly valuable for assessing spread along nerves. Positron emission tomography (PET) scans, often combined with CT (PET/CT), can help identify metabolically active cancer cells throughout the body, including distant sites. These advanced imaging techniques are not routinely used for all SCC cases due to the low overall risk of spread. Consistent follow-up care after initial treatment is important, especially for individuals with high-risk features, to monitor for any signs of recurrence or metastasis.